Six inch silver sector, late 18th century.
© Science Museum / Science & Society Picture Library
A sector with attached set square, made and signed by Jese Ramsden, London. Sectors were used from the end of the 16th century until the mid 19th century for calculations involving proportion. They were engraved with logarithmic and trigonometric lines, and lines for drawing and calculating surfaces and volumes, all radial from the centre of the hinge.